Multihop Wireless Networks: Opportunistic Routing

8.5 Multirate Link-Quality Measurement

To make our MGOR protocol work, we need to estimate the link quality (PRR) at different data rates. We propose a broadcast-based multirate link-quality measurement scheme in this section. This link quality measurement scheme also serves for multirate neighborhood management.

Recall that there are k different data rates. Each node maintains k neighbor tables corresponding to the k data rates. The jth table stores the bidirectional PRR information about its neighbors at rate Rj. For every τ second, each node broadcasts k “Hello” messages with each transmitted at a different data rate, e.g. 11 mbps, 5.5 mbps, and 2 mbps. Whenever a node n receives a “Hello” message sent from a node m at rate Rj, it will include node m into the corresponding neighbor table. Two events drive the updating of PRRmn at Rj on node n: one is the periodical updating event set by node n. For example, every tu seconds node n will update PRRmn. We denote this event as T. The other is the event that node n receives a “Hello” packet sent from m at rate Rj. We denote this event as H.

The exponentially weighted moving average (EWMA) method (Woo and Culler 2003) is used to update PRR information. Since at each rate, the PRR is updated according to the same EWMA mechanism, we only describe the EWMA at a particular rate as follows. Let PRRmn be the current estimation made by node n, lastHello be the time stamp of the last event H, Nm be the number of known missed “Hello” packets ...